Such swivel eyes are used in particular in instances where use is made of a plurality of eyes fixed to the load and where these eyes are connected to a single lifting member (e.g. a hook) by slings or chains. In such a case, the direction of the lifting slings or chains is inclined relative to the axis of the fixing member, and it is important that the plane of the annular part is oriented in the direction in which the pull force is applied to the eye, to prevent excessive forces across the plane of the eye and also to prevent any risk of excessive tightening, and above all loosening, of the fixing screw. Orientation of the eye must therefore be able to adapt to this lifting force direction, without the need for swivelling of the fixing screw, or without the application of a tightening or loosening torque thereto.
Typically, a lifting eye comprises a swivel body joined to a fixing member by a swivel linkage, and an attaching loop integral with the swivel body and generally hinged.
One major objective for manufacturers of lifting eyes is to guarantee user safety, primarily by the dimensions of the eyes, the choice of materials and the manner of manufacture. However, guaranteeing safety also involves guaranteeing eye integrity.
One drawback of known lifting eyes lies in their dismantlability. This is because one or more essential elements of an eye, in particular at the level of the swivel linkage, may be dismantled and, without this being apparent to the user, replaced by unsuitable elements or elements of lower quality. The user of a lifting eye of this type will therefore always be concerned that the eye may have been modified, without his or her knowledge, in such a way as to reduce the performance levels quoted by the manufacturer, so diminishing safety.
In this context, certain manufacturers have taken measures to limit the possibility of dismantling the eye.
EP1069067 and EP2361870 for example describe swivel eyes typically comprising a swivel element generally annular in shape, known as an attaching ring or loop, mounted on a body in which a bore is formed, and a screw fixing member extending into the bore. The screw fixing member comprises a head serving as a stop for the body and a threaded or tapped part for allowing fixing thereof by screwing into a tapped hole or onto a threaded shank integral with the load to be lifted. The lifting slings or chains may be connected to the swivel loop by insertion therein of a hook, shackle, carabiner etc.
In the eye of EP1069067, the swivel body is attached to a fixing bolt, and held between the bolt head and a flanged bushing fixed to the bolt. For increased safety, the flanged bushing is shrunk onto the bolt shank.
In the eye of EP2361870, the fixing member extends into a bore in the eye body and cooperates with a bushing and an anti-loosening washer.